The tear film normally includes a three layer structure: a lipid layer, a middle aqueous layer, and a mucinous layer. The lipid layer is the outermost layer and derived from the secretions of the Meibomian glands. It is likely composed of 2 phases: a thin polar phase adjacent to the aqueous-mucin phase and a thick nonpolar phase associated with both the polar phase and the air interface (McCully and Shine, Tr. Am. Soc. Vol. XCV, 1997). The middle aqueous layer is provided by the major and minor lacrimal glands, and contains water-soluble substances. The innermost mucinous layer is composed of glycoprotein, mucin, and overlies the corneal and conjunctival epithelial cells. The epithelial cell membranes are composed of lipoproteins and thus generally hydrophobic. When any of the tear film components is deficient, the tear film will break up, and dry spots will form on the corneal and the conjunctival epithelium. Deficiency of any of the three components (aqueous, mucin or lipid layers) may result in dryness of the eye.
In recent years, a great of efforts have been made to develop contact lenses capable of delivering comfort agents. For example, U.S. Pat. Nos. 4,045,547, 4,042,552, 5,198,477, 5,219,965, 6,367,929 and 6,822,016, 7,279,507 and commonly owned co-pending U.S. patent application publication Nos. 2006/0079598A1 and 2006/0251696A1 (herein incorporated by reference in their entireties) disclose that leachable wetting agents can be incorporated into a lens formulation for making the contact lenses, to improve the surface hydrophilicity and/or wearing comfort of contact lenses.
Another example is to incorporate into contact lenses one or more bioactive agents the release of which is triggered by one or more tear components produced by the eye when the devices comes into contact with the tears, as disclosed in a commonly owned co-pending U.S. patent application publication No. 2008/0124376A1 (herein incorporated by reference in its entirety).
However, there are no contact lenses capable of delivering hydrophobic comfort agents which are the constituents or the likes of the tear film lipid layer and can strengthen and stabilize the tear film lipid layer and alleviate the dryness of the eye. Therefore, there exists a need for contact lenses capable of delivering hydrophobic comfort agents in a sustainable manner over an extended period of time.